Former U.S. Sen. Scott Brown of Massachusetts speaks during the 11th Annual Keeping the Dream Alive dinner commemorating the anniversary of Martin Luther King Jr.’s death, April 4, 2013 in Nashua, N.H. Declaring that he’s likely not done with politics, Mr. Brown from Massachusetts refused to rule out a run for office in New Hampshire. (AP Photo/The Telegraph, Will Wrobel)

AP

Democrats sprang into action following reports that former Massachusetts Sen. Scott Brown found a buyer for his home in Wrentham, Mass., and is planning to move to New Hampshire, fueling talk that he will enter the Senate race against incumbent Sen. Jeanne Shaheen, a Democrat.

Mr. Brown already owns a vacation home in New Hampshire, and his frequent visits to the state, coupled with his creation of a political-action committee there and a donation of $10,000 to the state party, have attracted Democrats’ attention. Sen. Kirsten Gillibrand (D., N.Y.) sent an email Tuesday morning rallying support for Ms. Shaheen, as she had done in April just after Mr. Brown opened the door to a New Hampshire campaign.

The Democratic National Committee posted an online ad on Craig’s List Monday night, poking fun at Mr. Brown as a “politician for hire” in Boston, Manchester, N.H., or Des Moines, Iowa.

ActBlue, a PAC that serves as an online fundraiser for Democratic candidates, urges visitors to the site to join Sen. Elizabeth Warren (D., Mass.), who defeated Mr. Brown in 2012, in supporting Ms. Shaheen. The contributions website states, “Let’s show Scott Brown: If he decides to run against Jeanne Shaheen, we’ll be there once again to stop him.”

Ms. Shaheen’s seat is seen as vulnerable due to her support of the Affordable Care Act, whose botched rollout has hurt several Democratic candidates running for re-election in 2014.

Mr. Brown told local officials that he planned on registering to vote “soon” in Rye, N.H., town clerk Beth Yeaton said Tuesday. “It sounded like he was planning on doing it relatively quickly,” she said.

In a sign he’s watching events in D.C. closely, Mr. Brown tweeted his criticism of the budget deal Tuesday morning, saying it “unfairly cuts benefits for veterans.” The tweet, which urged senators to “stand up for our military by voting against this bill,” went out moments after the Senate voted by a wide margin to advance the legislation.

Republicans have actively been pushing Mr. Brown to join the Senate race, as polling shows the former Massachusetts senator has the best shot of all Republican contenders to win the seat. A poll taken in September, just before the troubled health-care rollout began, showed Mr. Brown trailing Ms. Shaheen by just four percentage points.

Ending Spending, an outside group that advocates fiscal restraint, began airing an ad on cable and broadcast television Tuesday criticizing Ms. Shaheen for telling state residents they could keep their health insurance under the new law. Another conservative group, Citizens for a Strong New Hampshire, ran similar ads in June targeting the senator’s support of the health care law.

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